Human liver alcohol dehydrogenase exists in multiple molecular forms, the number and distribution of which vary from person to person. Recently we discovered a new and distinctive molecular form of the enzyme which is present prominently in livers with high activity. Notably, it is absent in livers of low ethanol oxidizing activity, suggesting that it serves a major role in hepatic elimination of ethanol. By means of affinity chromatography, we have now separated this molecular form which is more anodic than the other forms on starch gel electrophoresis and purified it to homogeneity. Its physical properties are similar to those of other molecular forms already known. However, it is inactive towards methanol, and its Km for ethanol is as much as 100 times that of the other forms. Hence, it may contribute significantly to alcohol elimination, particularly at high alcohol concentrations when the other enzyme species are saturated. Additional catalytic features of this form are under study as well as the nature of the genetic relationship between it and the others through dissociation and recombination experiments. These studies may provide a molecular basis of understanding for normal and abnormal variations of ethanol metabolism in man.